Answers

Best Answer: Several points.
A) Why are you asking in the cycling (bicycle) section and not the automotive section?

B) If the wheels were larger or the TIRES? You could put a 15" wheel & a 16" wheel side-by-side, but...depending on the size and sidewall "aspect ratio" of the tires, they could measure the same height & diameter. Example... A tire P225/75R/15 will be about the same height as a tire P225/65R/16. The "aspect ratio" of the 15" tire has a sidewall 75% of the width. The 16" tire has an aspect ratio of 60%. The sidewall is 60% of the width.

C) They already started doing this several years ago. I worked at Good-Year dealers back in the late '70s & early '80s. A small car back then took a P155/80R/13 tire. Many small cars today have 14", 15" and even 16" wheels. But the aspect ratio is usually a LOT smaller today for a low profile tire resulting in better handling & better cornering. Tires today also have a higher psi rating - pounds per square inch - resulting in lower rolling resistance.

Larger wheels on a bike have many desirable factors. For example I have a 26" and a 29" bike. My 29" bike can get out of control when rolling down hills.

Bigger wheels negotiate bumps better, but in the case of a car, they would create more drag, and less efficiency.

The large rims with low profile tyres are about appearance, and low class attitude. The ride is terrible, and noisy. They might handle better on a race track, but offer nothing on city streets. Note that the low class people who buy them are usually the same people who illegally bump loud bass. You often see them parked in driveways where welfare recipients live.

all other things - tire design, tire pressure, road surface etc - being equal, then a wheel with a bigger working diameter would indeed roll easier.
The effect also depends on how coarse or smooth the surface is.
The smoother the surface, the lesser the advantage of going to bigger wheels.
Bigger wheels also get heavier, and begin to interfere with other features of vehicle design. The currently used sizes are a good all-round compromise that is unlikely to change much.

The most important contact between a vehicle and the ground is the tire. Tire construction and type can make a difference in efficiency more than wheel size. An example: My friend and I were out for a ride. We were both riding similar bikes, and more importantly we were both using the exact same make and model of wheels. However, he prefers tires that offer better puncture protection while I like tires made to provide the least rolling resistance. We arrived together at the top of a hill. We started down together. The hill was only about 400 meters long, yet at the bottom I was almost 50 meters ahead of him. He is about 10 pounds heavier than I am so he should have had an advantage over me. Tire design can make more of a difference than wheel size. When you coast past someone on a downhill you have no idea what sort of tires they have, or whether their tires are properly inflated for maximum efficiency.

From an engineering perspective your logic isn't even close. One of the few things a bicycle and a car have in common is they're both vehicles. It's kind of like comparing apples to oranges.

So what may make a bicycle faster won't necessarily make a car faster. Also making a car faster doesn't mean improved fuel economy. Speed and fuel economy are two totally different things from an engineering perspective.

A good way to test your theory is the only variable can be wheel diameter.

A lot of controlled conditions would be necessary.

A down gradient on an inside track to factor out wind conditions.

Gravity propulsion only. Kind of like soap box racing. To do this the chain would have to be removed and the crank locked into one position like 3:00, 9:00

The bikes only difference would be wheel diameter. The hubs, tires, bike design etc would have to be the same.

The same rider would have to ride all the bikes and have an electronic time keeper.

In the end you'll probably find wheel diameter plays only a small role when it comes to speed.

The bike in back always goes faster, due to wind resistance. Try an experiment with yourself, and a friend with a similar bike with similar wheels. Try with one of you in front coasting downhill, then switch positions and try again.